1. Field of the Invention
The present invention relates to drum-type shears for cutting high-speed strip, especially hot strip slabs, and more particularly to a drum-type shear having a blade that is carried in a rotatable blade drum and is selectively movable out of the blade drum and into a cutting position at a desired cutting time.
2. Description of the Related Art
Drum-type shears which can be used to crop and divide strip material, especially hot strip slabs, are known. Such shears operate as high-speed shears, i.e. the drums accelerate from a standing start to rotate at the passage speed of the rolled strip or slab material in approximately 0.9 drum rotations, cut the rolled material and then decelerate. At strip bandwidths of greater than about 1300 mm and strip speeds of approximately 3 m/sec, a limit is reached above which the enormous energy required for driving these shears can no longer be generated. In order to accelerate and decelerate the flywheel moments of the rotating masses, approximately 2000 kw of power must be provided in a short time period. When secondarily controlled hydraulic motors are used, the corresponding pump capacity for this power must also be made available. Even if a cut occurs only once every 10 minutes and acceleration/deceleration is needed then for only 0.5 seconds each time, the expense of the additional equipment required to accelerate and decelerate the cutting shears is extremely large.
As a rule, high-speed shears are adequate for conventional production processing of single slabs of material with rolled material speeds of up to about 3 m/sec, because it is not necessary to cut at the coiling speed when rolling out single slabs.
In various new production processes, however, the operations of strip casting and forming are linked, so that strip is produced and cut in a continuous series of process steps. As a consequence, slabs weighing 20 tons are no longer rolled individually into coils, as was done in the past. Instead, an almost continuous strand is produced, formed and cross-cut in front of the coiling device. Strip speeds of 4 to 10 m/sec and above are thereby achieved, requiring corresponding outputs from the shears located in front or upstream of the coiler.
So-called two-drum shears for cutting high-speed rolled material are well known as such. In two-drum shears, the rolled material to be cut passes between two separate blade drums which rotate at a peripheral speed corresponding to the passage speed of the rolled material. The blades or blade holders holding the blades are mounted in the blade drums in a radially movable fashion and are moved radially outward from the drum for cutting of the material. Unlike the aforementioned high-speed shears, two-drum shears do not need to be accelerated in a very short time to the passage speed of the rolled material; rather, the blade drums can be initially brought up to speed and then maintained at an undisturbed high speed, after which the blades may be used to cut the material at the desired time.
When the passage speed of the rolled material is extremely high, it has also been proposed--as in DE-AS 12 81 794--to advance the blades from within the two-drum shears into the cutting position by means of a shock or pressure-wave piston.
The primary problems with known two-drum shears for cutting of high-speed rolled material are related to the mechanical guidance of the blades or blade holders and to the hydraulic action of the pistons that activate the blades. Often, the mechanical system and hydraulic system are not able to absorb the high cutting forces of 110 to 300 tons that typically occur during cutting, especially in the case of thicker rolled material, so that the use of two-drum shears is limited to thinner rolled material or narrow strips or wire.
There is accordingly a need for a high-speed drum-type shear that can crop and divide strip material at strip speeds of 10 m/sec and above. There is also a need for a high-speed drum-type shear that can accelerate and decelerate at speeds corresponding to the strip speed without requiring additional and expensive equipment. There is further a need for a high-speed drum-type shear having a mechanical system for deploying the cutting blade and that is capable of withstanding cutting forces of up to 300 tons.